Uncertainty Management Planning: Turning Failure into Opportunity

Mark Ian Smithard¹ and Antonio M'Panzu^2
1 Chevron North America Upstream, Houston, TX
² Chevron International Exploration & Production, Luanda, Angola

Block 14, Angola has been a success story for the contractor group comprising Sonangol P&P, Chevron, ENI, GALP, and Total. Success has not come without its ups and downs, but planning for uncertainty has allowed Chevron to be in the position to turn misfortune to an advantage.

Tombua-3 was the third well drilled in the Tombua complex. It was permitted as a twin directional borehole, with the objective of testing up to 7 prospective channels in the western and eastern fault blocks. The well planning process recognised uncertainties in the spill of one of the main objectives, and as such it was imperative that the twin well was designed with evaluation of the central fault block via a third leg a possibility.

Whilst drilling the second leg (TMB3-ST1), the BHA became stuck after penetrating the main objective, and several thousand feet of borehole had to be abandoned. Faced with the decision of which direction to drill around the fish, the exploration team was ready with an upside objective that could not have been reached by the initial plan given the prime objectives.

The side-track was drilled below TMB3-ST1, penetrated the remaining objectives, and with the assistance of drillers, the well trajectory was dropped sufficiently to successfully tag the over-bank limits of the upside objective - a previously untested interval.

Partners were quickly consulted, and a third leg was interactively designed to appraise the central fault block for remaining reserves in the prime objectives, whilst properly testing the newly discovered interval.